Recently, a class of cell surface proteins have been described in both plants and animals that are involved in pathogen perception, MHC class II trans-activation, inflammation and the regulation of apoptosis (Inohara, N., Nunez, G, Cell, Death, Differ., 6(9):823–4, (1999); Inohara, N., Koseki, T., del, Peso, L., Hu, Y., Yee, C., Chen, S., Carrio, R., Merino, J., Liu, D., Ni, J., Nunez, G, J. Biol, Chem. 21., 274(21):14560–7, (1999); Inohara, N., Nunez, G, Cell, Death, Differ., 7(5):509–10, (2000); Harton, J A., Ting, J P, Mol, Cell, Biol., 20(17):6185–94, (2000); Dixon, J., Brakebusch, C., Fassler, R., Dixon, M J. Hum, Mol, Genet. 12., 9(10):1473–80, (2000)). All of these proteins are modular in nature containing one or several domains that function in caspase recruitment (CARD), nucleotide binding and protein-protein interactions. Proteins within this group have also been found to play a role in cell adhesion during various developmental processes.
A common theme in all of these proteins are the presence of a leucine-repeat repeat (LLR) in the carboxy terminus of the polypeptide chain. LLRs are short protein modules characterized by a periodic distribution of hydrophobic amino acids, especially leucine residues separated by hydrophilic residues [Sean, 1996]. The basic structure of the repeat is as follows:X-L-X-X-L-X-L-X-X-N-X-a-X-X-X-a-X-X-L-Xwhere X is any amino acid, L is leucine, N is asparagine and “a” denotes an aliphatic residue. The asparagine at position 10 can be replaced by cysteine, threonine or glutamine. The average repeat length is 24 amino acids but it can vary between 22 to 29 amino acids, though some LRR motifs have been reported to be at short as 20 amino acids. The motif often consists of leucine or other aliphatic residues at positions 2, 5, 7, 12, 16, 21, and 24 and asparagine, cysteine or threonine at position 10. X-ray structure determination of LRR motifs suggests that each LRR is composed of a beta-sheet and an alpha-helix. The largest subfamily of proteins that contain a leucine-rich domain are extracellular proteins having the following motif: LxxLxxLxLxxNxLxxLPxxOFxx, where“x” is any amino acid and “O” is a non-polar residue (Kajava, J. Mol. Biol. 277: 519 (1998)).
In transmembrane proteins, LLRs and their flanking sequence always occur in the presumed extracellular portions. In these situations the LLRs are generally flanked on either side by cysteine-rich regions. In general, these cysteines are present in the oxidized disulphide link form. An example of a transmembrane protein containing a LRR is Toll, a Drosophila gene the functions in establishment of dorsal-ventral patterning. Dominant, ventralizing mutants have been described that map to the cysteine-rich regions surrounding the LLR domain [Schneider, 1991]. Thus, the cysteine regions associated with LLRs act to regulate receptor activity. The LLRs themselves within the Toll protein have been shown to function in heterotypic cell adhesion, a process required for proper motoneuron and muscle development [Halfon, 1995]
Another Drosophila LLR containing transmembrane protein, 18 wheeler, which is regulated by homeotic genes also promotes heterophilic cell adhesion in cell migration events during development (Eldon, E., Kooyer, S., D'Evelyn, D., Duman, M., Lawinger, P., Botas, J., Bellen, H, Development., 120(4):885–99, (1994)). Mammalian CD14, which binds lipopolysaccharide (LPS), and signals through NF-κB, is thought to have analogies to the Toll signal transduction pathway. CD14 also contains a region of LLRs that have been shown in deletion mutants to be responsible for LPS binding.
Slit is another LLR containing Drosophila secreted protein that functions in the development of the midline glial cells and the commissural axon tracts the cross the midline. This is presumably accomplished by cell adhesion events (Jacobs, J R, J. Neurobiol., 24(5):611–26, (1993)). Mammalian homologues of Drosophila slit have been shown to bind the heparan sulfate proteoglycan, glypican-1 (Liang, Y., Annan, R S., Carr, S A., Popp, S., Mevissen, M., olis, R K., olis, R U, J. Biol, Chem. 18., 274(25):17885–92, (1999)). In general, heparan sulfate proteoglycans have been shown to accummulate in Alzheimer's disease brains and specifically, glypican-1 is component of both senile plaques and neurofibrillary tangles (Verbeek, M M., Otte, Holler, I., van, den, Born, J., van, den, Heuvel, L P., David, G., Wesseling, P., de, Waal, R M, Am. J. Pathol., 155(6):2115–25, (1999)). Heparan sulfate proteoglycans are also implicated in the regulation of cytokine signaling in B cells through the activation of CD40 (van, der, Voort, R., Taher, T E., Derksen, P W., Spaargaren, M., van, der, Neut, R., Pals, S T, Adv, Cancer, Res., 79:39–90, (2000)).
p37NB is a 37 kDa LRR protein identified in human neuroblastoma cells (Kim, D. et al. (1996) Biochim. Biophys. Acta 1309: 183–188). Northern blot hybridization and RT-PCR studies show that p37NB is differentially expressed in several neuroblastoma cell lines. A related LRR protein, PRELP, is characterized as a 42 kDa secreted protein (Bengtsson, E. et al. (1995) J. Biol. Chem. . . . 270: 25639–25644). PRELP consists of 10 LRR motifs ranging in length from 20 to 26 residues with asparigine at position 10. Northern analysis shows differential expression of PRELP in various tissues.
In addition, leucine-rich repeat containing proteins have also been implicated in various aspects of protein-protein interaction, such as cell-to-cell communication and signal transduction (for a review, see Kobe and Deisenhofer, TIBS 19: 415 (1994); Kobe and Deisenhofer, Curr. Opin. Struct. Biol. 5: 409 (1995); Kajava, J. Mol. Biol. 277: 519 (1998)). Proteins that contain an LRR motif include hormone receptors, enzyme subunits, cell adhesion proteins, and ribosome-binding proteins.
A subfamily of the LRR superfamily, referred to as the Small Leucine Rich Proteoglycan family, illustrates the critical functions fulfilled by proteins containing an LRR motif. Members of this subfamily are believed to play essential biological roles during inflammation and cancer invasion, a regulatory role in collagen fibril formation, suppression of the malignant phenotype of cancer cells, and an inhibition of the growth of certain normal cells (see, for example, Iozzo, Annu. Rev Biochem. 67: 609 (1998)).
Kajava, et al., J. Mol. Biol. 277: 519 (1998), divided the LRR superfamily into subfamilies characterized by different lengths and consensus sequences of the leucine-rich repeats. Based upon this structural analysis, Kajava concluded that LRR proteins of different subfamilies probably emerged independently during evolution, indicating that proteins with the LRR motif provide a unique solution for a wide range of biological functions.
LLR containing proteins have been identified in prokaryotes, plants, yeast and mammals. Although such proteins were initially thought to be secreted proteins, it is now appreciated that they inhibit a variety of cellular locations and participate in a diverse set of critical functions in development and cellular homeostasis.
Such LRRs, being extracellular, are capable of directing protein-protein interactions with other receptors involved in apoptosis, inflammation and immune responses. LLR containing proteins may also bind other extracellular ligands derived from infectious agents and participate in the triggering and or modulating immune responses.
The recently cloned Nogo receptor (Fournier et al., 2001), is a 473 amino acid protein (Genbank Accession number: AAG53612). This receptor is brain specific, is associated with the cell surface via a GPI-linkage, and possesses eight leucine rich repeat domains and a cysteine rich LRR carboxy-terminal flanking domain. Expression of this receptor confers responsiveness to Nogo-66, which binds to Nogo receptor, in unresponsive cells. Identification of small molecules that block the inhibitory effects of Nogo on axonal regeneration can be used for therapeutic treatment of neurodegenerative conditions.
Using the above examples, it is clear the availability of a novel cloned leucine-rich repeat containing protein provides an opportunity for adjunct or replacement therapy, and are useful for the identification of leucine-rich repeat containing protein agonists, or stimulators (which might stimulate and/or bias leucine-rich repeat containing protein action), as well as, in the identification of leucine-rich repeat containing protein inhibitors. Hence it can be reasoned that agonists and antagonists for these LLR containing proteins will be useful for therapeutic purposes
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of HLLRCR-1 polypeptides or peptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the HLLRCR-1 polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of HLLRCR-1 polypeptides or peptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the HLLRCR-1 polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.